To improve maintainability, Japanese Patent Application Publication (JP-A) No. 06-193573 discloses a screw compressor having a coupling casing coupling a compressor body and a motor, in which a motor shaft and a rotor shaft are fastened by shaft couplings in the coupling casing.
The screw compressor is of the vertical type in which the motor is disposed above the compressor body. The screw compressor having the above configuration is also of the horizontal type in which the motor is disposed in a side of the compressor body.
In the screw compressor of the horizontal type having the coupling casing, part of the weight of the motor is applied, as a load, to the motor side coupling portion of the coupling casing. In addition, since the motor and the compressor body vibrate during operation, this causes a force to act on the coupling casing. In particular, the stress in the vertical direction is large.
To further improve the maintainability of the shaft couplings in the coupling casing, a work hole is provided in the coupling casing.
When the work hole is provided in the coupling casing, the shear rigidity in the vertical direction of the coupling casing is significantly reduced. Reduction in rigidity leads to larger vibration and breakage. As a simple solution for this, to compensate for the rigidity, the thickness of the tubular portion of the coupling casing is increased, or a radial rib is provided in the tubular portion of the coupling casing. However, both of increase in the thickness of the tubular portion and addition of the radial rib make the weight of the material larger, resulting in cost increase.